Opal

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Opal is a hydrated silica form of silica (SiO ₂ Ã, Â n H ₂ O); its water content can range from 3 to 21% by weight, but usually between 6 and 10%. Due to its amorphous nature, it is classified as a mineraloid, unlike the crystalline form of silica, which is classified as a mineral. It is stored at relatively low temperatures and can occur in cracks of almost all rock types, most commonly found with limonite, sandstone, rhyolite, napal, and basalt. Opal is Australia's national gemstone.

There are two broad opal classes: valuable and common. The precious opal displays color games, ordinary opals do not. Play-of-color is defined as a "pseudochromatic optical effect that produces colored light flashes of certain minerals, because they change in white light." The precious internal structure of opal causes it to break the light, resulting in a color game. Depending on the conditions under which it is formed, the opal may be transparent, translucent or opaque and the background color may be white, black or almost any color of the visual spectrum. Black opal is considered the rarest, while white, gray and green are the most common. In addition, the opal may show adularescence, a form of color game.

Video Opal

valuable Opal

The valuable opal shows the interaction of internal color variables, and although it is a mineraloid, it has an internal structure. On a microscopic scale, valuable opals are composed of silica balls of 150 to 300 nm diameter in tightly closed lattices. It was shown by J. V. Sanders in the mid-1960s that the ordered silica ball produced an internal color by causing disturbance and diffraction of light through the opal microstructure. The regularity of the size and packaging of these balls determines the quality of a valuable opal. Where the spacing between regularly packaged spheres is about half the wavelength of the visible light component, the light of the wavelength can be diffraction from the lattice made by the stacked plane. The colors observed are determined by the distance between the plane and the orientation of the plane in connection with the incident light. This process can be explained by the Bragg diffraction law.

Visible light can not pass through the bulky thickness of the opal. This is the basis of optical bandgap in photonic crystals. The idea that opals are photonic crystals for visible light was expressed in 1995 by the Vasily Astratov group. In addition, microfractures can be filled with secondary silica and form a thin lamella inside the opal during freezing. The term opalescence is generally and erroneously used to describe this unique and wonderful phenomenon, which is properly called color play. In contrast, opalescence is applied correctly on the look like common opch or potchal which is cloudy and turbid. Potch does not show color games.

For the use of gemstones, most of the opals are cut and polished to form a cabochon. The "solid" opal refers to a polished stone made entirely of precious opal. Opal is too thin to produce "solid" can be combined with other materials to form an attractive gem. An opal doublet consists of a relatively thin opal layer, supported by a dark-colored material layer, most commonly iron, ordinary dark or black opal (potch), onyx, or obsidian. Darker support emphasizes color games, and produces a more attractive look than lighter potch. An opal triplet is similar to a doublet, but has a third layer, the dome cap of a clear quartz or plastic on it. The lid is high polish and serves as a protective coating for the opal. The top layer also acts as a magnifying glass, to emphasize the opal color game underneath, which often has lower quality. Therefore the Triplet oplet has a more artificial appearance, and is not classed as a valuable opal. The valuable opal jewelry application can be somewhat limited by the opal sensitivity to heat mainly because of its relatively high water content and a tendency to scratch. Combined with modern polishing techniques, the opal doublets produce effects similar to black opal or stone blocks at a fraction of the price. Doublet opal also has the added benefit of having the original opal as a visible and untouched layer, unlike the triplet oplet.

Maps Opal

General opal

In addition to the jewelry varieties that exhibit color games, other common opal types include dairy opals, turquoise to greenish (which can sometimes be a gem quality); opal resin, a yellow honey with a resin luster; wooden opal, caused by the replacement of organic matter in wood with opal; menilite, which is brown or gray; hyalite, the brightest colored opal sometimes called the Muller glass; geyserite, also called silica sinter, is deposited around hot springs or hot fountains; and diatomite or diatomaceous earth, shell accumulation or diatom tests.

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Other opal varieties

The fire opal is a transparent opal for translucency, with warm body colors from yellow to orange to red. Although it usually does not show any color games, sometimes a rock will show bright green sparks. The most famous source of fire opals is the state of QuerÃÆ' Â © taro in Mexico; This opal is usually called a Mexican fire opal. An opal fire that does not show color games is sometimes referred to as an opal jelly. Mexican opal is sometimes cut in their rhyolite host material if it is difficult enough to allow cutting and polishing. This type of Mexican opal is referred to as the Cantera opal. Also, a kind of Mexican opal, referred to as a Mexican water opal, is a colorless opal that shows a bluish internal sheen or gold sheen.

Opal Girasol is a term that is sometimes wrong and should not be used to refer to a fire opal, as well as a kind of transparent semitransparent semitransparent type from Madagascar that displays asterism, or star effects, when properly cut. However, the actual girasol opal is a kind of opal hyalite that exhibits a bluish or glowing light that follows the light source around it. This is not a color game as seen on the precious opal, but rather the effect of microscopic inclusion. It is also sometimes referred to as water opal, too, when it's from Mexico. The two most famous locations of this type of opal are Oregon and Mexico.

The Peruvian Opal (also called the blue opal) is a semi-opaque blue-green stone found in Peru, often cut to insert a matrix in a more opaque stone. It does not feature color games. Blue opal also comes from Oregon in the Owyhee region, as well as from Nevada around the Virgin Valley.

Opal is also formed by diatoms. Diatoms are microscopic, shelly, aquatic organisms. When they die and form a layer at the bottom of a lake or bay or sea, their shell, made of opal, forms a "grain" for diatomite rocks. This sedimentary stone is white, opaque, and chalky. Diatomite has several industrial uses such as filtration or adsorption because it has fine particle size and highly porous nature, and gardening to increase water adsorption.

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History

Opal is rare and very precious in ancient times. In Europe it is a gem that is valued by the nobility. Until the opening of a massive deposit in Australia in the 19th century, the only known source was? Ervenica outside the Roman border in Slovakia.

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Source

Opal Australia is often cited as accounting for 95-97% of the world's valuable opal supply, with the state of South Australia accounting for 80% of world supply. Recent data indicate that the world's precious supplies of opal may have changed. In 2012, Ethiopian opal production is estimated at 14,000 kg (31,000 pounds) by the United States Geological Survey. USGS data from the same period (2012), revealed that Australian opal production to $ 41 million. Because of the unit of measurement, it is impossible to directly compare Australian and Ethiopian opal production, but these and other data suggest that the traditional percentage given for Australian opal production may be overestimated. However, the validity of the data in the USGS report seems to contradict Laurs et al. and Mesfin, which estimates Ethiopia's opal output in 2012 (from Wegal Tena) to just 750 kg (1,650 pounds).

Australia

The town of Coober Pedy in South Australia is the main source of opal. The world's largest and most valuable gem opal "Olympic Australis" was discovered in August 1956 at the "Eight Miles" opal field in Coober Pedy. Weighing 17,000 carats (3.4 kg, 7.5 pounds) and 11 inches (280 mm) long, with a high 4 ³ / ₄ in (120 mm) and width 4 ¹ / ₂ in (110 mm ). The Opal Mintabie field, located approximately 250 km (160 mi) northwest of Coober Pedy has also produced large crystal opals and rarer black opal. Over the years, it has been sold overseas incorrectly as Coober Pedy opal. Black opal is said to be some of the best examples found in Australia.

Andamooka in South Australia is also a major producer of opal matrix, crystal opal, and black opal. Another Australian city, Lightning Ridge in New South Wales, is the main source of black opal, opals containing dark backgrounds (dark gray to blue-black color game displays). Boulder opal consists of the compression and filling of fractures in a dark silica iron stone matrix. It is found sporadically in western Queensland, from Kynuna in the north, to Yowah and Koroit in the south. The largest number is found around Jundah and Quilpie in South West Queensland. Australia has also blurred the remains of fossils, including dinosaur bones in New South Wales, and sea creatures in South Australia.

Ethiopia

Although it has been reported that North African opals were used to build tools as early as 4000 BC, the first report published by Ethiopian gems of opal emerged in 1994, with the invention of valuable opals in Menz Gishe District, North Shewa Province. Opal, found mostly in the form of nodules, is derived from a volcano and is found primarily in ripe layers of rhyolite. Shewa Province opal is mostly dark brown and tend to crack. These qualities make it unpopular in gem trading. In 2008, a new opal deposit was found about 180 km north of Shewa Province, near the town of Wegel Tena, in Wollo province, Ethiopia. Opal Wollo Province is different from the earlier Ethiopian opal findings that look more like Australian and Brazilian sedal opals, with a bright background and often a vibrant color. Opal Wollo Province, more commonly referred to as the "Welo" or "Wello" opal, has become the dominant Ethiopian opal in gems trading.

Virgin Virgin Valley, Nevada

The Virgin Valley opal field in Humboldt County in northern Nevada produces various types of black crystal, crystal, white, fire, and opal lemon. The black fire opal is an official Nevada gemstone. Most valuable opals are partial wood substitutes. The valuable opal is hosted and is found in the horizon or bentonite zone beneath the surface that is considered a "lode" deposit. Opal that has been out of deposit on the spot is alluvial deposits and considered. Teeth, bones, fish, and the head of an old Miocene-snake have been found. Some opals have high water content and can dry and crack when dried. Virgin Valley's largest producer mines are the famous Rainbow Ridge, Royal Peacock, Bonanza, Opal Queen and WRT Stonetree/Black Beauty. The largest rough black opal at the Smithsonian Institution, known as the "Roebling opal", came out of the tunnel section of the Rainbow Ridge Mine in 1917, and weighed 2,585 carats (517.0 g; 18.24 oz). The largest polished black opal at the Smithsonian Institution comes from the Royal Peacock opal mine in Virgin Valley, weighing 160 carats (32 g, 1.1 oz), known as the "Black Peacock".

Mexico

Opal takes place in significant quantities and variations in central Mexico, where mining and production centers are in the country of QuerÃÆ'Â © taro. In this region the opal deposits are located mainly in the mountains of three municipalities: Colon, Tequisquiapan and Ezequiel Montes. During the 1960s to the mid-1970s, QuerÃÆ' Â © taro mine was heavily mined. Opal miners today report that it is much easier to find quality opal with lots of fire and color play back then, whereas today the quality gem opal is very hard to come by and orders hundreds of US dollars or more.

The oldest quarry in QuerÃÆ' Â © taro is Santa Maria del Iris. The mine was opened around 1870 and has been reopened at least 28 times since then. There are currently about 100 mines in the area around QuerÃÆ'Â © taro, but most of them are now closed. The best opal quality comes from the Santa Maria del Iris mine, followed by La Hacienda la Esperanza, Fuentezuelas, La Carbonera, and La Trinidad. Important deposits in Jalisco state were not discovered until the late 1950s.

In 1957, Alfonso Ramirez (from QuerÃÆ' Â © taro) accidentally discovered the first opal mine in Jalisco - La Unica, located in the area outside Tequila volcano, near Huitzicilapan farm in Magdalena. In 1960 there were about 500 known opal mines in this region alone. Another area in the country that also produces opals (of lower quality) is Guerrero, which produces opal opals similar to opals from Australia (some of these opals are carefully treated with heat to improve their color so high-quality opal from this area may suspected). There are also several small opal mines in Morelos, Durango, Chihuahua, Baja California, Guanajuato, Puebla, MichoacÃÆ'¡n, and Estado de MÃÆ'Ã… © xico.

Other locations

Another source of white opal or opal cream in the United States is Spencer, Idaho. The high percentage of opals found there occurs in thin layers.

Other significant deposits of valuable opals around the world can be found in the Czech Republic, Canada, Slovakia, Hungary, Turkey, Indonesia, Brazil (in Pedro II, PiauÃÆ'), Honduras (more precisely in Erandique), Guatemala and Nicaragua.

In late 2008, NASA announced it had found an opal deposit on Mars.

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Synthetic Opal

Opal of all varieties has been experimentally and commercially synthesized. The discovery of the ball structure ordered from valuable opal caused its synthesis by Pierre Gilson in 1974. The resulting material can be distinguished from natural opals by its regularity; under magnification, the color patch looks set in the pattern of "lizard skin" or "chicken wire". Furthermore, synthetic opals do not fluoresce under ultraviolet light. Synthetics are also generally lower in density and are often highly porous.

Two synthetic opal producers are Kyocera and Inamori of Japan. Most so-called synthetics, however, are more accurately called "artificial opal", because they contain substances not found in natural opals (such as plastic stabilizers). The artificial opal that is seen in antique jewelry is often thwarted glass, "Slocum stone" based glass, or later plastic materials.

Other studies in makroporous structures have produced highly ordered materials that have optical properties similar to opals and have been used in cosmetics.

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Local atomic structure opal

The opal ball grilles that cause interference with light are several hundred times larger than the basic structure of crystalline silica. As a mineraloid, there is no unit cell that describes the opal structure. However, opals can be roughly divided into those that show no sign of the crystal framework (opal amorphous) and opal showing the beginning signs of the crystalline order, commonly called cryptocrystalline or opal microcrystalline. Dehydration experiments and infrared spectroscopy have shown that most of H ₂ O in the formula SiO ₂ Ã, Â · n H ₂ O opal is present in the familiar form of molecular water clusters. The water molecule is isolated, and the silanol, a structure such as SiOH, generally forms a proportion that is lower than the total and can be near the surface or defect inside the opal.

The low pressure polymorphic structure of anhydrous silica comprises a full angle tetrahedra framework of SiO ₄ . Higher temperature polymorphisms of cristobalite and tridymite silica are often the first to crystallize from amorphous anhydrous silica, and the local structure of microcrystalline opal also appears closer to cristobalite and tridymite than quartz. The tridymite and cristobalite structures are closely related and can be described as hexagonal and cubic sealed layers. It is therefore possible to have a medium structure in which irregular layers are stacked.

Microcrystalline opal

Opal-CT has been interpreted as consisting of clumped cristobalite groups and tridymites on very short, long scales. The opal scope in opal-CT itself is made of small nanocrystalline blades of cristobalite and tridymite. Opal-CT is sometimes further divided into literature. The water content can be as high as 10% by weight. Lussatite is a synonym. Opal-C, also called lussatine , is defined as consisting of a local sequence of? -cristobalite with many interference stacking. The typical water content is about 1.5% by weight.

Noncrystalline opal

Two major categories of noncrystalline opal, sometimes simply referred to as "opal-A", have been proposed. The first is an opal-AG consisting of silica aggregates, with water filling the space between them. The valuable opal and potch opal are generally varieties of this, the difference being in the regularity of the ball size and the packaging. The second "opal-A" is an AN-op or amorphous silica glass containing water. Hyalite is another name for this.

Noncrystalline silica in silica-containing sediments is reported gradually transformed into opal-CT and then opal-C as a result of diagenesis, due to increased overburden pressure on sedimentary rocks, as some stacking disorders are removed.

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Etymology

The word 'opal' is adapted from the Latin term opalus , but the origin of this word is a matter of debate. However, most modern references suggest it is adapted from the Sanskrit word ÃÆ'ºpala .

References to gems are made by Pliny the Elder. It is recommended to be adapted from Ops, Saturn's wife and the goddess of fertility. The Saturnalia portion devoted to Ops is "Opalia", similar to opalus .

Another general claim that this term is adapted from the Ancient Greek word, opallios . It has two meanings, one related to "seeing" and forming the basis of English words like "opaque"; the other is "other" like "alias" and "alter". It is said that opalus combines this usage, which means "to see the color change". However, historians note that the first appearance of opallios did not occur until after the Romans took over the Greek states in 180 BC, and they had previously used the term "paederos .

However, the argument for the Sanskrit origin is strong. This term first appears in Roman references around 250 BC, at which time opal is rewarded above all other gems. Opal is supplied by merchants from the Bosporus, who claim that the gems are supplied from India. Before this stone was named by various names, but this fell out of use after 250 BC.

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Historical superstitions

In the Middle Ages, opal was regarded as a stone that could provide great fortune because it is believed to have all the virtues of each gemstone whose color is represented in the opal color spectrum. It is also said to give a translucent if it is wrapped in fresh bay leaves and held in hand. After the publication of Sir Walter Scott's Anne of Geierstein in 1829, opals earned a disadvantageous reputation. In Scott's novel, the Baroness of Arnheim wore an opal charm with supernatural powers. When a drop of holy water falls into the talisman, the opal turns into a colorless stone and the Baroness immediately dies. Because of Scott's novel popularity, people began associating opal with bad luck and death. Within a year of Scott's novel publication in April 1829, opal sales in Europe fell by 50%, and remained low for the next 20 years or so.

Even recently at the beginning of the 20th century, it was believed that when a Russian saw an opal among the other items offered for sale, he could not buy anything else, because the opal was believed to contain an evil eye.

Opal is considered a birthstone for people born in October.

Example

• Olympic Australis, the largest and most valuable gem opal in the world, is found in Coober Pedy
• The Andamooka Opal, presented to Queen Elizabeth II, also known as the Queen's Opal
• The Addyman Plesiosaur from Andamooka, "the best known opalization framework on Earth"
• The burning of Troy, the now-lost opal given to Josà © Ã… © de Beauharnais by Napoleon I of France and the first opal named
• The Flame Queen Opal
• Halley's Opal Comet, the world's largest raw black opal
• Although the clock faces upstairs information standing at Grand Central Terminal Manhattan, New York, it's often said opal, they're actually opalescent glass
• Opal Roebling, Smithsonian Institution
• Galaxy Opal, listed as "The Largest Opal in the World" in the Guinness Book of Records 1992
• The Rainbow Virgin, "the best crystal opal specimen ever dug"
• The world's largest black opal
• Australian fires, assumed to be "the best uncut opal" "

See also

• Cacholong
• Foil opal
• Opalite
• Optical phenomenon

References

Further reading

• Eckert, Alan (1997). The World of Opals . Wiley. ISBN: 9780471133971. OCLCÃ, 36352362. External links
  • Farlang opal Hist. References Locality, anecdotes by Theophrastus, Isaac Newton, Georg Agricola etc.
  • ICA's Opal Page: International Colored Stone Association
  • Opal Fossils from the South Australian Museum Retrieved 19 October 2016.

  Source of the article : Wikipedia